The present invention relates to a drive unit including a first actuator and a second actuator for driving a drive target.
Drive units for driving a drive target by first and second actuators have conventionally been known. An example of the drive units is disclosed by Patent Document 1.
The drive unit disclosed by Patent Document 1 includes a stage as a drive target, two first actuators for driving the drive target in the predetermined X direction and two second actuators for driving the drive target in the predetermined Y direction orthogonal to the X direction.
Each of the first and second actuators is constituted of a piezoelectric element which is substantially rectangular when viewed in plan, and generates a longitudinal vibration and a bending vibration. The first and second actuators are arranged to be in contact with the stage. In this state, the piezoelectric elements are allowed to generate the longitudinal and bending vibrations to cause a friction force between the actuators and the stage, thereby moving the stage. More specifically, the travel amount of the stage by the first actuator and that by the second actuator are adjusted so that the stage can be moved in a desired direction between the X and Y directions.
However, in moving the stage in only one of the X and Y directions, for example, in only the X direction, the second actuator is kept in a halt state and only the first actuator is driven. In this case, even though the second actuator is in a halt state, the second actuator is biased against the stage with a certain biasing force, and thus a friction force between the second actuator and the stage hinders the movement of the stage in the X direction by the first actuator.
According to the drive unit disclosed by Patent Document 1, in moving the stage in only one of the X and Y directions, e.g., in only the X direction, the first actuator is driven to generate a composite vibration of the longitudinal vibration and the bending vibration, and the second actuator is driven to generate only the longitudinal vibration. Since the direction of the longitudinal vibration is orthogonal to the stage, the second actuator is periodically separated from the stage while the first actuator is driven. In this way, the friction force between the second actuator and the stage is reduced so that the second actuator does not hinder the movement of the stage in the X direction by the first actuator.
Patent Document 1: Published Japanese Patent Application No. H11-235063